Welding is a fabrication process used to join two or more materials together. Welding is utilized in almost every industry, including manufacturing processes and process control plants. In general, welding involves melting two work pieces together and adding a filler material to form a pool of molten material that cools or dries to form a joint. The work pieces are often compositions of metals or metal alloys and the filler material is often a metal or metal alloy. Many different types of welding exist such as, for example, gas tungsten arc welding, gas metal arc welding, flux-cored arc welding, shielded metal arc welding, etc.
When welding together two dissimilar metals and/or metal alloys, metallurgical problems can arise. For example, when welding two work pieces of steel alloy, such as grade 22 steel (e.g., ASTM A387) and grade 91 steel, a steep gradient exists with regard to the chromium content or concentration in the different steels. Grade 22 steel has a chromium content of about 2.25 percent (%) by weight while grade 91 steel has a chromium content of about 9.00% by weight. During post-weld heat treatment and/or during service of the work pieces in a relatively high temperature area, carbon diffusion occurs between the grade 22 steel and the grade 91 steel due to the different chromium contents. Carbon diffusion causes a reduction in strength and/or creep resistance in the lower-chromium metal (i.e., the grade 22 steel). Even when using a filler material having a chromium content that is between the chromium contents of the grade 22 steel and the grade 91 steel, the chromium content gradient still results in carbon diffusion between the grade 22 steel and the grade 91 steel.
The figures are not to scale. Instead, to clarify multiple layers and regions, the thickness of the layers may be enlarged in the drawings. Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts.